A few years ago Patrick Collison remarked there are fewer younger founders today. Ben Horowitz and Martin Casado agree that's what the hardware era looks like, for now: "If you look at Elon or Travis Kalanick, their companies when they were young were software companies. Even those guys, the best guys, needed some experience to graduate to the more elaborate domains." "When you're learning how to build a company, it's hard enough if you completely understand the product. If you don't…